CVE-2026-78663
CRITICAL
CVSS 9.1
Published: 2026-10-08
Modified: 2026-10-09
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Description
The HTTP/2 server can refund connection-level flow control twice for the same data: Once when a client resets a stream (refunding data for any sent-but-unread portion of the stream), and again when a request handler reads the buffered data. A malicious client can exploit this to bypass the configured connection-level flow control limit (MaxReceiveBufferPerConnection). Total buffered data is still limited by the concurrent stream limit and stream-level flow control.
Quick Facts
| CVE ID | CVE-2026-78663 |
| CVSS Score | 9.1 |
| Vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H |
| Published | 2026-10-08 |
| Exploited | No |
| CISA KEV | No |
| PoC | Not public |